Temperature and power supply calibration

ABSTRACT

This document discusses, among other things, a temperature and power supply calibration system configured to compensate for temperature and supply voltage variation in MEMS or other circuits using representations of positive and negative supply voltages and first and second base-emitter voltages, wherein the second base-emitter voltage is a scaled representation of the first base-emitter voltage.

CLAIM OF PRIORITY

This application claims the benefit of priority under 35 U.S.C. §119(e)of U.S. Provisional Patent Application Ser. No. 61/798,517, titled“PLL-based Demodulation Method for a MEMS Gyroscope,” filed on Mar. 15,2013, which is incorporated by reference herein in its entirety.

BACKGROUND

In certain examples, circuit performance or output can be affected byvarious external conditions, such as changes in operating temperature.In response, various solutions have been developed, including, forexample, temperature sensors configured to provide temperature, incertain examples, allowing for calibration of the circuit to thespecific determined operating temperature.

OVERVIEW

This document discusses, among other things, a temperature and powersupply calibration system configured to compensate for temperature andsupply voltage variation in MEMS or other circuits using representationsof positive and negative supply voltages and first and secondbase-emitter voltages, wherein the second base-emitter voltage is ascaled representation of the first base-emitter voltage.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the invention. The detaileddescription is included to provide further information about the presentpatent application.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 illustrates generally a system including a temperature-to-digitalconverter (TDC) configured to determine a temperature using a ratio ofbase-emitter voltage (V_(BE)).

FIG. 2 illustrates generally an example sensor configured to sense bothtemperature and supply voltage information.

FIG. 3 illustrates generally an example supply voltage conditioningcircuit.

FIG. 4 illustrates generally an example diagram including a voltage andtemperature sensor configured to compensate an output of a sensor (e.g.,a MEMS sensor) output.

DETAILED DESCRIPTION

Microelectromechanical systems (MEMS) include small mechanical devices,fabricated using semiconductor fabrication techniques, that performelectrical and mechanical functions, sensitive to, among other things,motion, acceleration, or orientation in various forms. Examples of MEMSsensors include, among other things, accelerometers, gyroscopes,magnetometers, etc. MEMS, due to their size and mechanical nature, canbe sensitive to, among other things, even minor variations intemperature or supply voltage.

The present inventors have recognized, among other things, systems andmethods for calibrating sensors or circuits, MEMS or otherwise, forvariation in supply voltage, reducing the sensitivity of the sensor orcircuit to changes in supply voltage during operation. For example, adifference between a positive and negative supply, or a change (Δ) insaid differences can be determined and subsequently used to compensatethe output of the sensor or circuit.

Many existing sensors and circuits (e.g., MEMS sensors, etc.) include atemperature sensor to sense temperature information and compensate forvariation in an output signal due to temperature. For example, FIG. 1illustrates generally a system 100 including a temperature-to-digitalconverter (TDC) 110 configured to determine temperature informationusing, at least in part, first and second base-emitter voltages(V_(BE)). Because V_(BE) of a transistor varies with temperature, aratio of V_(BE) can be used to provide temperature information. Theratio can be accomplished using transistors with scaled currentdensities, multiple transistors in parallel, etc. In operation, actualtemperature can be determined using a ratio of a proportional toabsolute temperature (PTAT) change in V_(BE) to a temperature flatbandgap voltage. The determined temperature information can be used toreduce the temperature coefficient of the associated sensor or circuit.

The TDC 110 can be configured to receive a single unit of V_(BE)(V_(BE)UNIT) at a first input and a multiple unit of V_(BE) (V_(BE)MULT)(e.g., 10×V_(BE)UNIT, etc.) at a second input, to determine adifferential output using a differential amplifier 111, and to provide adigital output signal representative of the difference using an outputcircuit 116. In certain examples, the TDC 110 can include feedbackcircuits 112, 113, a TDC conditioning circuit 115 including, forexample, one or more resistors, capacitors, switches, or one or moreother desired circuits or components configured to condition the signalsprovided to the differential amplifier 111. In an example, the TDCconditioning circuit 115 can be controlled using a control signal(CTRL_(TDC)), in certain examples, including a clock signal, etc. Incertain examples, when a digital output is desired, the output circuit116 can include an analog-to-digital converter (ADC). In other examples,the output circuit 116 can be configured to provide an analog outputrepresentative of the difference between the first and second inputs.

The present inventors have recognized that, in certain examples, acombined temperature and supply voltage sensor can be realized using asingle differential amplifier circuit, receiving both temperatureinformation and supply voltage information. In certain examples, anexisting temperature sensor can be modified to detect both temperatureinformation and supply voltage information.

In an example, an uncalibrated sensor can provide an uncorrected outputX. Many error coefficients, such as temperature or supply voltageinformation, can be corrected using a linear correction factor, e.g.,Y=m*X+b, where m is the scale and b is the offset. In an example, bothoffset and scale can be corrected using the techniques disclosed herein.In other examples, other higher-order correction techniques can be usedto provide a compensated output.

In an example, the differential amplifier circuit can continue toreceive temperature information while receiving supply voltageinformation. In other examples, the differential amplifier circuit canreceive temperature information at a first time and supply voltageinformation at a second, different time, using, for example, differentcontrol signals and one or more switches. In an example, as a bandgapvoltage can be developed as a function of V_(BE), the supply voltage canbe detected as, for example, a ratio of a bandgap voltage, without theuse of a separate traditional analog bandgap voltage reference.

FIG. 2 illustrates generally an example sensor 200 configured to senseboth temperature and supply voltage information, the sensor 200including a differential amplifier 111 similar to that illustrated inthe example of FIG. 1. The supply voltage sensor 200 can include asupply voltage conditioning circuit 120 including, for example, one ormore capacitors, switches, or one or more other desired circuits, andcan be configured to receive a positive supply voltage (V_(DD)) at afirst input and a negative supply voltage (V_(SS)) at a second input. Inan example, the sensor 200 can be configured to receive V_(DD) andV_(SS) as well as V_(BE)UNIT and V_(BE)MULT. In an example, the supplyvoltage conditioning circuit 120 can be controlled using a controlsignal (CTRL_(VDD)), in certain examples, including a clock signal, etc.

Depending on the desired output, the output circuit 116 can include oneor more memory circuits (e.g., registers, flip-flops, non-transitorycomputer-readable storage media, etc.) or one or more other circuitsconfigured to condition the output of the sensor 200 to provide desiredoutput information. One example of such output is described, forexample, in FIG. 4.

As illustrated in FIG. 2, the components of an existing temperaturecircuit, such as that illustrated in the example of FIG. 1, can bemodified to provide the combined temperature and supply voltage sensor,for example, without requiring a traditional bandgap voltage reference,as a bandgap voltage can be estimated using V_(BE) and ΔV_(BE) of thetemperature sensor.

FIG. 3 illustrates generally an example supply voltage conditioningcircuit 120 including, for example, first, second, and third transistors121, 122, 123, first and second capacitors 124, 125, and a controlcircuit 126. The first and second transistors 121, 122 are configured toreceive V_(DD) and V_(SS), respectively, and the control circuit 126 isconfigured to receive CTRL_(TDC). In an example, using the controlcircuit 126, the first and second transistors 121, 122 can be configuredto sample V_(DD) and V_(SS) on the first and second capacitors 124, 125,respectively, and the third transistor 123 can be configured to dump thecharge on the differential amplifier 111 and feedback circuits 112, 113.Further, as used herein, V_(DD) and, in certain examples, V_(SS), canrefer to scaled representations of V_(DD) or V_(SS) (e.g., using avoltage divider, capacitor and switch, etc.).

FIG. 4 illustrates generally an example diagram 400 including a voltageand temperature sensor 104 configured to compensate an output of asensor 101 (e.g., a MEMS sensor) output. In an example, an existingsensor system 109 includes the sensor 101 and a signal conditioningcircuit 102. In existing systems, the output of the signal conditioningcircuit 102 is used. Other existing systems include a temperature sensorconfigured to adjust the output of the sensor 101 to correct for changesin the output due to temperature. However, the example of FIG. 4 furtherincludes a voltage and temperature sensor 104 configured to separatelydetect supply voltage information using V_(DD) (or a representation ofV_(DD)) at a first time and temperature information using V_(BE) at asecond time. Timing of the detection can be controlled, for example,using CTRL, which, in certain examples can include a simple clock signalor, in other examples, a more sophisticated custom control, depending ondesired output or performance.

The example diagram 400 further includes an example supply memory(V_(DD)MEMORY) 105 and an example temperature memory (TDCMEMORY) 106.Memory circuits 105, 106 can include, for example, simple memorycircuits such as a switch and capacitor, a transistor, a flip-flop, orone or more other simple circuits, or more complex memory circuits suchas a register, a flip-flop, a non-transitory computer-readable storagemedia, etc.

In an example, a difference between the voltage information andtemperature information can be taken at a difference circuit 107, and acorrection factor can be calculated using the bandgap voltage and ascale factor α (e.g., a scale factor representing the reduction fromV_(DD) to the representation of V_(DD), etc.) at calculation circuit108. Further, the output of the signal conditioning circuit 102 can beadjusted using the output of the calculation circuit 108 at summationcircuit 103 to provide a compensated output.

In other examples, one or more other calculations can be made. Forexample, the operations of the difference circuit 107 can be swapped,the difference circuit 107 can instead include a summation circuit orone or more other circuits, the calculation circuit 108 can beconfigured to perform one or more other operations, or the summationcircuit 103 can include a difference or one or more other circuits.

In certain examples, the summation circuits 103 can be omitted entirely,and the output of the calculation circuit 108 can be provided to thesignal conditioning circuit 102. In other examples, the outputs of oneor more of the voltage and temperature sensor 104, the memory circuits105, 106, the difference circuit 107, or the calculation circuit 108 canbe provided to the signal conditioning circuit 102 to provide acompensated output, such as by altering a scale or offset in a firstorder linear correction or one or more second- or higher-ordercorrection components.

An example implementation of the circuits illustrated, includingdigitally building the bandgap voltage using an existing TDC, forexample, as follows:

Assuming m_(temp) is the average sigma-delta (SD) output of atemperature sensor (from 0 to 1), such as that illustrated in FIG. 1, wecan provide the following:

(1−m _(temp))10ΔV _(BE) =m _(temp) V _(BE)  (Eq. 1)

where, V_(BG)=10ΔV_(BE). Therefore:

$\begin{matrix}{m_{temp} = {\frac{10\Delta \; V_{BE}}{\left( {V_{BE} + {10\Delta \; V_{BE}}} \right)} = {\frac{10\Delta \; V_{BE}}{V_{BG}}.}}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

If we add variable Y to the (1−m) measurement and Z to the mmeasurement, where Y and Z are αV_(DD) and −αV_(DD), respectively, theequations become:

$\begin{matrix}{{\left( {1 - m} \right)\left( {Y + {10\Delta \; V_{BE}}} \right)} = {m\left( {Z + V_{BE}} \right)}} & \left( {{Eq}.\mspace{14mu} 3} \right) \\{m = \frac{\left( {Y + {10\Delta \; V_{BE}}} \right)}{\left( {Y + Z + V_{BG}} \right)}} & \left( {{Eq}.\mspace{14mu} 4} \right) \\{m_{V_{DD}} = {\frac{\left( {\alpha \; V_{DD}} \right) + \left( {10\Delta \; V_{BE}} \right)}{V_{BG}}.}} & \left( {{Eq}.\mspace{14mu} 5} \right)\end{matrix}$

Therefore, all that is required to implement supply voltage correctionin digital with reference to V_(BG) is:

$\begin{matrix}{\frac{\left( {m_{V_{DD}} - m_{temp}} \right)V_{BG}}{\alpha} = V_{DD}} & \left( {{Eq}.\mspace{14mu} 6} \right)\end{matrix}$

Additional Notes and Examples

A system or apparatus can include, or can optionally be combined withany portion or combination of any portions of any one or more of theexamples or illustrations above to include, means for performing any oneor more of the functions described above, or a machine-readable mediumincluding instructions that, when performed by a machine, cause themachine to perform any one or more of the functions described above.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventor alsocontemplates examples in which only those elements shown or describedare provided. Moreover, the present inventor also contemplates examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

All publications, patents, and patent documents referred to in thisdocument are incorporated by reference herein in their entirety, asthough individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document, forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, or process that includes elements in addition to those listedafter such a term in a claim are still deemed to fall within the scopeof that claim. Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment, and it is contemplated that such embodiments can be combinedwith each other in various combinations or permutations. The scope ofthe invention should be determined with reference to the appendedclaims, along with the full scope of equivalents to which such claimsare entitled.

What is claimed is:
 1. A temperature and power supply sensitivitycalibration system, comprising: a differential amplifier having a firstinput configured to receive a first base-emitter voltage (V_(BE)), asecond input configured to receive a second base-emitter voltage, and anoutput configured to provide temperature information using the first andsecond base-emitter voltages; and a voltage conditioning circuitconfigured to sample representations of a positive and negative supplyvoltages and selectively provide the positive supply voltage sample tothe first input of the differential amplifier and the negative supplyvoltage sample to the second input of the differential amplifier,wherein the second base-emitter voltage is a scaled representation ofthe first base-emitter voltage, and wherein the power supply sensitivitycalibration system is configured to provide temperature and supplyvoltage information using the first and second base-emitter voltages andthe representations of the positive and negative supply voltages.
 2. Thesystem of claim 1, including a microelectromechanical system (MEMS)sensor, wherein the power supply sensitivity calibration system isconfigured to correct for temperature and supply voltage variation inthe MEMS sensor using the temperature and supply voltage information. 3.The system of claim 1, wherein the voltage conditioning circuit isconfigured to sample representations of the positive and negative supplyvoltages at a first time and provide the positive and negative supplyvoltage samples to the first and second inputs of the differentialamplifier at a second time.
 4. The system of claim 3, wherein thedifferential amplifier receives the first and second base-emittervoltages during both the first and second times.
 5. The system of claim1, wherein the voltage conditioning circuit includes: a first transistorconfigured to selectively couple the representation of the positivesupply voltage to a first capacitor; and a second transistor configuredto selectively couple the representation of the negative supply voltageto a second capacitor.
 6. The system of claim 5, wherein the voltageconditioning circuit includes a third transistor configured toselectively provide charge from the first and second capacitors to thefirst and second inputs of the differential amplifier.
 7. The system ofclaim 1, including a temperature-to-digital circuit (TDC) configured toreceive the first and second base-emitter voltages and to providedigital temperature information using the first and second base-emittervoltages.
 8. The system of claim 1, wherein the system includes anoutput conditioning circuit including an analog-to-digital converter(ADC), wherein the output conditioning circuit is configured to receivethe output of the differential amplifier, to store temperatureinformation in a first memory circuit and supply voltage information ina second memory circuit, and to provide a digital correction signalusing the stored temperature and supply voltage information.
 9. Thesystem of claim 1, including a microelectromechanical system (MEMS)sensor, wherein the output conditioning circuit is configured to correctfor temperature and supply voltage variation in the MEMS sensor usingthe temperature and supply voltage information.
 10. The system of claim9, wherein the output conditioning circuit is configured to subtract thetemperature information from the supply voltage information and add theresulting output to the MEMS sensor information.
 11. A power supplysensitivity calibration method, comprising: receiving a firstbase-emitter voltage (V_(BE)) at a first input of a differentialamplifier and a second base-emitter voltage at a second input of adifferential amplifier; providing temperature information using adifference between the first and second base-emitter voltages; andsampling representations of positive and negative supply voltages usinga voltage conditioning circuit; selectively providing the positivesupply voltage sample to the first input of the differential amplifierand the negative supply voltage sample to the second input of thedifferential amplifier using the voltage conditioning circuit; providingtemperature and supply voltage information using the first and secondbase-emitter voltages and the representations of the positive andnegative supply voltages, wherein the second base-emitter voltage is ascaled representation of the first base-emitter voltage.
 12. The methodof claim 11, including correcting for temperature and supply voltagevariation in a microelectromechanical system (MEMS) sensor using thetemperature and supply voltage information.
 13. The method of claim 11,wherein the sampling representations of the positive and negative supplyvoltages includes sampling representations of the positive and negativesupply voltages at a first time, and wherein the selectively providingthe positive and negative supply voltage samples to the first and secondinputs of the differential amplifier includes providing the positive andnegative supply voltage samples to the first and second inputs of thedifferential amplifier at a second time.
 14. The method of claim 13,wherein the receiving the first and second base-emitter voltagesincludes receiving the first and second base-emitter voltages duringboth the first and second times.
 15. The method of claim 11, wherein thesampling the representations of the positive and negative supplyvoltages includes: selectively coupling the representation of thepositive supply voltage to a first capacitor using a first transistor;and selectively coupling the representation of the negative supplyvoltage to a second capacitor using a second transistor.
 16. The methodof claim 15, wherein the selectively providing the positive and negativesupply voltages samples to the differential amplifier includesselectively provide charge from the first and second capacitors to thefirst and second inputs of the differential amplifier using a thirdtransistor.
 17. The method of claim 11, including providing digitaltemperature information using a temperature-to-digital circuit (TDC) andthe first and second base-emitter voltages.
 18. The method of claim 11,including: receiving output from the differential amplifier at an outputconditioning circuit; storing temperature information in a first memorycircuit and supply voltage information in a second memory circuit; andproviding a digital correction signal using the stored temperature andsupply voltage information.
 19. The method of claim 11, including:correcting for temperature and supply voltage variation in amicroelectromechanical system (MEMS) sensor using the temperature andsupply voltage information.
 20. The method of claim 19, including:subtracting the temperature information from the supply voltageinformation; and adding the resulting output to the MEMS sensorinformation.